Fogging devices, used to generate an insecticide fog, for example, and utilizing the pulse-jet (resonant intermittant combustion) principle, are well known in the prior art. An example of such a device is disclosed in Tenney et al, U.S. Pat. No. 2,857,332 and pulse-jet engine operation is there explained in some detail. A fogging apparatus utilizing a resonant, intermittant combustion device, a fuel supply, an insecticide supply and a starting device is disclosed in Curtis U.S. Pat. Nos. 3,151,454 and 3,993,582. The fuel feeding scheme of the early devices, such as disclosed in the Tenney et al patent, delivered fuel to the engine by aspiration from a constant level fuel supply.
Curtis U.S. Pat. No. 3,151,454 introduced pressurization of the fuel tank as a means for delivering fuel to the engine. The apparatus of the present invention is an improved version of such prior art devices characterized by positive pumping of the fuel supply using the combustion pulses of the engine to provide the pumping impetus and by the pressurization of a diaphragm-walled chamber, during the engine starting interval, to open the fuel inlet valve. In the apparatus of the present invention there is no pressurization of the fuel tank while the engine is in full operation, such pressurization occuring only during the short, initial starting interval. The fuel system of the apparatus responds rapidly to a change in air flow through the carburetor (caused, for example, by introduction of insecticide formulation into the engine exhaust stream) by correspondingly altering fuel flow. Proper operation of the fuel system is substantially independent of changes in the tilt angle or physical orientation of the apparatus. Flooding out of the combustion system by momentarily supplying too much fuel for existing air flow, a difficulty to which prior art devices are prone, is substantially eliminated in the apparatus of the present invention.